Micromanifold for powder cloud development



Feb. 17, 1959 P. G. ANDRUS ETAL MICROMANIFOLD FOR POWDER CLOUD DEVELOPMENT Filed NOV. 3. 1954 25 14 FIG! l i /22 POWDER CLOUD k 15 AIR on GAS CLOUD P %a? SUPPLY GENERATOR I I4 20 2 l 26 2a FIGS AIRORGAS SUPPLY INVENTORS,

PAUL G.ANDRUS, LEWIS E. WALKUP FMAASML ATTORNEY .radiation to which the lot this combined exposure and Unitedv States Patent MICROMANIF OLD FOR POWDER CLOUD DEVELOPMENT Application November 3, 1954, Serial No. 466,576 3 Claims. (Cl. 118-637) This invention relates in general to xerography'and in particular to the development of xerographic images.

In the art of xerography an electrostatic latent image is formed on an insulating surface, such as, for example, a photoconductive insulating surface, by the combined .action of an electric field applied through a photocon- \ductive material and action of light or suitable activating radiation on the photoconductive material to cause selective conductivity in accordance with the pattern of material is exposed. The result field is a pattern of electric charge known to the art as an electrostatic latent ;'image which is capable of utilization, for example, by deposition thereon of finely divided material, such deposition being known in the art as development.

It has been found by others in the art of xerography that an electrostatic latent image can be developed very satisfactorily by presenting to the image surface a cloud of charged powder particles with a conductive surface or'development electrode positioned very closely adjacent to the image surface, preferably at a distance therefrom in the order of about to of an inch or in some instances even somewhat closer than 3 inch.

material, across an area of norwhose smallest dimension is several inches or an area whose smallest dimension is a foot or more. The introduction of a cloud uniformly across this entire area in a development space in the order of $1 to 1 inch thick has obviously presented many serious problems. The other somewhat related problem is the fact that powder tends to deposit from the cloud on all available surfaces, including not only the image surface, but the surfaces of other members through which it passes, and such deposition results in irregular operation of the developing mechanisms. It is, therefore, desirable to pass the powder cloud through its turbulent zone immediately prior to introduction into the actual development space and to introduce the powder cloud to the development space simultaneously at a plurality of locations in order to reduce to a minimum the impairment'of results.

It is, accordingly, an accomplished object of the invention to provide new and improved development apparatus for xerographic images wherein a uniform cloud of particles is introduced simultaneously at a plurality of locations into an extremely fine development space between a xerographic image bearing surface and a closely adjacent development electrode.

It is another object of the invention to provide new development means, methods and apparatus for the depo sition of charged powder particles from a gas suspension onto an electric image.

It is still another object of the invention to provide in xerographic development apparatus means, methods and apparatus for simultaneously presenting to an extremely narrow development space at a plurality of locations, a freshly charged and deagglomerated cloud of powder particles and it is a related object of the invention to provide a new manifold for charging and deagglomerating such particles directly into an extremely narrow development space.

Additional objects of the invention will in part be obvious and will in part become apparent from the following specification and drawings in which:

Fig. l is an enlarged diagrammatic view in cross section of a portion of development apparatus in accordance with one embodiment of the invention;

Fig. 2 is an enlarged view partially in section of a micromanifold in accordance with one embodiment of this invention;

Fig. 3 is a schematic flow diagram illustrating the apparatus and process of one form of the present invention;

Fig. 4 is a diagrammatic view of development apparatus according to another embodiment of the invention;

Fig. 5 is a bottom cross section of a portion of the device shown in Fig. 4;

Fig. 6 is a front view of the exit end of the development zone structure of the apparatus shown in Fig. 4.

Referring to the figures, there is shown in Fig. 1 a cross section of a portion of development apparatus according to one embodiment of the invention. In this apparatus a xerographic plate 11 is suitably positioned in a device for development of the xerographic image. Desirably, as shown, the xerographic plate is placed face down in the development position so that only electrical forces rather than forces of gravity will cause deposition of powder material thereon. Directly below the xerographic plate is a development at an extremely close spacial relationship with respect to the xerographic plate by means of a plurality of spacers 13. In the preferred operation of the invention, the surface of the xerographic plate 11 and the surface of the development electrode 12 are placed as close together as possible with respect to ordinary machining practice and skill so that the two surfaces are relatively uniformly spaced apart over their entire area to permit the free flow therebetween of a cloud of finely divided particles. It has been found in practice that desirable spacing is in the order of about 4 inch since this spacing is relatively close and yet is within the realm of good manufac turing practice for the good presentation of surfaces substantially parallel with one another and substantially uniformly spaced across the entire area. It has further been found in practice that to achieve significant results this spacing must be less than about inch, preferably about 1 inch or closer, and may be as narrow as a minimum spacing which will permit the passage of the cloud of powder particles between the two surfaces without channeling or irregularity in flow the surfaces.

Leading into the space between the xerographic plate 11 and'the development electrode 12 is a conduit 14 operably connected to a source of powder cloud and adapted electrode 12 spaced caused by irregularities of and positioned to feed the .powder cloud into this development space. Desirably, the other end of the conduit is connected to a suitable powder cloud generator as illustrated hereinafter.

The xerographic plate 11 according to this form of the invention is a metallic or like conductive member having a substantially fiat and smooth surface with a photosensitive layer 1 coating the surface. Desirably, according to usual practice, borders and the like around the photosensitive layer may be bare and electrically conductive. According to present commercial practices, thephotosensitive layer 15 is a coating of vitreous appearing selenium which has been deposited on the metallic surface under carefully controlled conditions to form a mirror-smooth selenium surface characterized by being a ,photoconductive insulator and generally having a thickness between'about 0.0005 and 0.01 inch. It is to be understood, however, thatinsulating surfaces in general, on which an electrostatic image exists, may be appropriately employed for development.

t Suitably positioned adjacent to the active development area and desirably in the uncoated border at one end or side of the xerographic plate is a micromanifold illustrated in greater detail in Fig. 2. This micromanifold is a very thin block of solid material having a plurality of holes, capillaries or tubes 21 extending therethrough. The thickness of this block or micro rnanifold is designed and constructed to be'the same as the spacing between the xerographic plate 11 and the development electrode 12. Thus, for example, if these two surfaces are to be spaced apart by 4 inch, then the micromanifold like: wise is ,4 inch thick. In illustration, one form of micromanifoldjll which has been constructed and operated was' 1 inch long and contained ducts, each 0.0035 inch and spaced 0.031 inch apart; the micromanifold widthfand therefore, the duct length was 0 .1 inch and the thicknesswas. 0.025 inch, this thickness likewise being the spacing between the xerographic plate and the devel-:

opedeleetrode. The micromanifold withithese dimensions was suitably employed for the development of a xero-. graphic image on a xerographic plate having a size of 1 inch by 5 inches of sensitive area, the micromanifold be-.

ing placed adjacent to the shorter edge-of the plate. The plate consisted of a conductive or metal backing member liavin'g alayer ofvitreous selenium "of about 0.002 inch thick on its surface whereby the spacing between the sur: face, of the seleniurniandthe development electrode was and tuozs inch;

It is"ap'p'arent that the manufacture of a micromanh fold of thesediinension's containing holes of the. desired thickness a sing eagewise through a relatively thin body, is a critical manufacturing operation. One particularly valuable and easy wa of producing a structill of thede'sired endear dimensions and specifications is as follows. Two accurately machined strips of brass, each 1 inch long, inch wide and inch thick were prepared and a grid was prepared with 32 wires to the inch, the wire's'havingfa diameter of 0.0035 inch. The two strips of brass. were placed on. either side of this grid under a force of about 20,000 pounds and in this position were carefully "soldered together. The wires then 'w'ere'pulled out from between the brass s 'trips leav-v iiig ducts of likediameter in the solder between the b'rass.'

The dimensions of the micromanifold may be adjusted or varied as desired, keeping;'in mind-theneed to maintain'a minimum thickness so as to achieve minimum spacing between the Xerographic'plate and the development electrode, and keeping in mind the need for having. a pluralityof very fine ducts passing edgewise through the. manifold. "For the'developrnent of extremely lai ge size pictures it is desirable'to employer 'subst'antiallylonger manifoldhaving a plurality of ducts at leastsorne of which are positioned near the ends and others desirably near the. center of the micrornanifold Preferab1y, the

micromanifold is of substantially equal length with re- ,spect to the width of the surface being developed, and the ducts are generally uniformly spaced along the length of the manifold. It is now believed that superior results are achieved in this invention with the ducts so close together that the gas from the ducts merges into a .unitary stream before the gas reaches laminar flow.

Referring to Fig. 3 the operation of the invention may be more readily determined. In this embodiment of the invention a xerographic plate 11 having a photosensitive layer 15 on one surface thereof is placed closely adjacent to a development electrode 12, optionally mounted within a development cabinet 23. A filter 24 at one end of the development cabinet permits discharge of air from the cabinet with retention of the developer material or finely divided particulate material which is to be deposited on the xerographic image. Desirably, means are provided for applying an electric potential difference between the backing member of the Itemgraphic plate 11 and the development electrode 12. These means may include, for example, a battery 22 or similar D. C. power source connected through a potenv tiometer 25' to one or the other of the xerographic plate or the development electrode. The xerographic plate 11 and development electrode 12 are suitably spaced apart by means of spacer l3 and micromanifold 20 which are placed between thetwo surfaces. The micromanifold is located andpositioned to feed directly into the develop? mefit Sp t-fie between the development electrode, 12 and the photosensitive coating 15 of the Xerographic plate.

On the opposite side of the micromanifold away from the development space a tube or conduit 14 leads from a cloud generator 2 6 to the development electrode and into the space behind the rnicromanifold. A suitable air or s pp u e 27 i adapted t f ed through. conduit 28 into the cloud generator to cause-formation of a-cloud of suspended powder or other particulate material which is then led through the rnicrornanifold and into the de-. velopment zone.

In operation a xerographic plate is suitably charged, for example, by spraying ions thereon from a corona discharge electrode and is exposed to a pattern of activating radiation which is to be recorded, thus forming an elect tro static latent image on the Xerographic plate. The Plate is then placed in position over the development electrode, as illustrated in Fig. 3. The air or gas supply source 27 is energized forcing compressed air or gas through the.

cloud generator to produce a suspension of developer particles in air, andthis cloud suspension is passed under turbulent conditions through the duct; 21 in micromania fold 20, emerging therefrom in a chargcdand deagglomer ated state into the development space adjacent tothe im= age bearing surface 15. The bias or potential on the xerographic plate or development electrode is; set as ale-.-

sired and the finely divided particles are deposited in configuration in accordance with the electrostatic-latent;

image, thus forming a developed xerographic picture.

In the present specification, the term micromanifold is used to relate to a block or body of solid material. hay,

ing passing therethrough a plurality of capillary ductsof extremely fine diameter. These ducts are. as fine as is; consistent with-the turbulent flow therethrough of a cloud;

of powder particles and are designed to produce a high degree of turbulence with a minimum of danger of,

plugging or blocking of the; ducts. It is intended that the microlnanifold be use'd with a finely divided powder hav,

ing' particles generally in the size range of about 1 or. several microns andless frequently with the average particle size being a small fraction of l micron. The duct; des r bly ould e s t an. .0 nc inorsi ve turbulent flow at reasonable flow. rates and a v ly is illihe order; of less than 0.005 inch with; an opt I 0.003 inch. Relatively wide variation is permissiblein the g hp e fit ll t s b eved. hat a. uc length can diamete beli d .tof e about 10.0021

interior of the cabinet.

of as much as 1 inch is operable. However, operation at reasonable air pressures and reasonable rates of air flow make somewhat shorter ducts desirable and a duct length of 0.1 inch has been found to be eminently satisfactory as well as easier to construct, and for practicable air pressures a duct length of up to /5 inch is believed to be the maximum. The micromanifold should be as long and should have as many ducts as is found desirable according to best operational and manufacturing practice, the ducts preferably being less than inch apart.

In forming the cloud suspension it is desirable to use air or other gas which can conveniently be passed through the system to form the powder cloud and to permit charging thereof. In addition to ordinary compressed air, it has been found particularly convenient to employ a preformed cartridge containing a gas such as Freon 12 which is believed to be a normally gaseous fluorine substituted hydrocarbon, the cartridge containing this gas at a pressure of at least'SO p. s. i. -With the use of Freon 12 and a finely powdered charcoal, excellent xerographic images have been developed. As far as can be determined, other gases under pressure are likewise equally satisfactory.

The desired rates of flow can readily be determined by those skilled in the art. The following conditions, however, have been employed with satisfactory results with Freon 12 as the suspending gas. To insure turbulent flow through the small capillary tubes of the micromanifold a Reynolds number of 8,000 was selected for the flow. By mathematical calculation, it was determined that the Reynolds number should equal to approximately 330 times the flow rate in liters per minute divided by the diameter of the duct in inches, thus calling for the flow rate of 0.085 liter per minute in the device specifically described. In continuing the mathematical calculations, several arbitrary rules of thumb can be used to gain additional information about the size and construction of the manifold. For example, in the development of a square inch picture, such as a 4 x 5 picture area, it has in the past been found desirable to employ a gas fiow of about 12 liters of gas per minute. It is apparent, therefore, that for a flow of 0.085 liter per minute through each duct that the development of a 20 square inch picture under comparable conditions calls for about 140 ducts across a4 inch width, or about ducts per inch for optimum operation. Similarly, based on this same figure of 0.085 liter per minute and taking an arbitrarily assumed gas pressure of 60 p. s. i., it can be determined mathematically that an optimum limit for practical operation calls for a duct length of not over about /2 inch. Since a gas pressure of about 60 p. s. i. is readily obtained and is a convenient basis of operation there follows directly a preferred limit of duct lengths of not over about /2 inch when operating under these conditions although increased pressure permits a corresponding increase in duct lengths. It is understood that similar determinations can be made with respect to air and other gases as well as for the Freons.

Referring to Figs. 4, 5 and 6 there is illustrated semidiagrammatically a further embodiment of the invention. According to this embodiment, developing mechanism is housed in a suitable cabinet preferably having a door 41 secured to the walls of the cabinet by suitable hinges 42 or the like for convenient access into the Mounted within the cabinet is a development electrode 44 having a plurality of spacers 45 optionally at the exit end thereof. Positioned on the development electrode at the entrance end is a micromanifold 20 desirably extending across the width of the development electrode. Preferably shoulders or runners 46 extend upwardly along the sides of the development electrode to serve as side supports and dust seals between the development electrode and a xerographic plate placed thereon.

A xerographic plate 11 is adapted to be placed on the development electrode supported by the shoulders,

spacers and manifold so as to form a development space between the electrode and the plate. As thus formed, the development space is a long, extremely narrow, flat chamber extending between the plate and the develop-; ment electrode having its entrance portion at the manifold 20 and having its exit portion between spacers 45 at the opposite end of the plate. The sides are sealed against escaping gas or dust by shoulders 46.

Also mounted within cabinet 40 is an air or gas supply 48 from which a tube or conduit 49 leads through control valve 50 to a slit-like nozzle or series of nozzles 51. This slit-like nozzle is adapted and directed to feed a jet of air directly toward the ducts in manifold 20. If feasible, the jet of air from the jet or series of jets covers the entire length of this manifold. Mounted to pass between the nozzle 51'and the manifold 20 is a power impregnated ribbon 52 desirably passing through ribbon guides 53. The ribbon preferably is carried on a feed reel 54 and is adapted to be passed between the nozzle and the manifold to a take-up reel 55 which preferably is spring or motor driven in order to move the ribbon at a controlled rate. In practice, the nozzle 51 and manifold 20 are relatively close together, thereby the ribbon 52 will pass almost in direct contact with the manifold. Thus, a jet of gas from the jet 51 strikes against the ribbon 52 and carries a supply of powder in gas suspension through the manifold into the development zone and out from the opposite end thereof. A filter 57 is positioned in the adjacent wall of the cabinet 40 to permit exit passage of the gas while collecting any powder particles that are not deposited in the development zone or elsewhere in the cabinet. In use and operation a xerographic plate which has been properly charged and exposed to form an electrostatic latent image thereon, is placed in position on the manifold 20 and spacers 45 and the gas supply and ribbon are activated. Desirably Valve 50 is controlled or controllable from outside the cabinet as also is the drive mechanism for reel 55. As these two mechanisms, the valve and the ribbon drive, are activated, a stream of powder bearing gas is passed under turbulent conditions through the manifold 20 whereby the powder particles are substantially uniformly charged and are substantially deagglomerated. Passing from the micromanifold, these particles thereupon are deposited on the xerographic plate in conformity with the electrostatic latent image. After development is complete, the mechanism is stopped and the developed plate may be removed for other utilization as desired.

It is apparent that the invention is adapted to operate with any suitable source of powder cloud generator, but as is shown in Figs. 4 to 6, a ribbon generator is peculiarly suited to the manifold disclosed herein, and one embodiment of the invention specifically contemplates the combination, as disclosed, of manifold and powder impregnated ribbon. In such case, a cloth ribbon or the like is preloaded with a finely divided powder material such as a pigmented resin, colored powder, charcoal or the like, and the ribbon is then placed in the development apparatus as illustrated.

It will be understood that numerous variations and modifications may be made within the scope of the invention and that the invention is to be limited only by the appended claims.

What is claimed is:

1. Apparatus for developing an electrostatic image on an electrically insulating layer comprising in combination an electrically conductive development electrode having a surface conforming to the shape of said layer, means to support said layer in opposite, spaced, substantially parallel relation above said development electrode to provide a development zone between said electrode and said layer, a strip-like block positioned at one end of the development electrode and extending substantially completely across one edge of the development zone, a.

,7 multiplicity of fine ducts positioned along. the length of sa'idb'lock andext'ending' through the block from the development zone, the diameter of the ducts being less than- 0'.020-in ch, means for generating and flowing a gas suspension of finely-divided development material ,from

said generatingmeans sequentially through said'ducts and the development zone, the restricted diameter of the ducts producing turbulent flow in the powder cloud serving to simultaneously deagglornerate the development material and electrically charge thermaterial through triboelectric contact with the walls of said ducts.

-2. Apparatus for developing an electrostatic image on an electrically insulating layer comprising in combination an electrically conductive development electrode having a surface conforming to the shape of said layer, means to support saidlayer-in opposite, spaced, substantially parallel relation above said developmentelectrode at a distance of'nomore than As-inch to provide a developmerit-zone between saidelectrode and said layer, a striplike block positioned at one end of the development electrode and; extending substantially completely across one edge of the development zone, a multiplicity of fine ducts positioned; along the length of saidblock and extending through the block} from the development zone, the diameter of the ducts being less'than 0.020-ineh, means for generating and flowing a gas suspension of finely-divided development material from said generating means sequentially through saidducts and the development zone, the restricted diameter of the ducts producing turbulent flow" in the powder cloud serving to simultaneously deagglo'merate the development; material and electrically chargethe material through triboelectric' contact with the walls of said duct.

"3. Apparatus for developing an electrostatic image on an electrically insulating layer;comprising in combination an. electrically conductive development electrode having a surfaceconforming tothe shape of said layer, means to support saidlayer in opposite, spaced, substantially parallel relation above said development electrode at a distance-of no more than, -inch to provide a development zone between said electrode and said layer, a striplike block positioned at one end of the development electrode and extending substantially completely across one edge of the development zone, a multiplicity of fine ducts positioned along the length of said block and extending through the block from the development zone, the diameter of the ducts being about 0.002 to 0.003-inch, means for generating and flowing a gas suspension of finelydivided' development material from said generating means sequentially through said ducts and the development zone, the restricted diameter of the ducts producing turbulent flow in the powder cloud serving to simultaneously deagglomerate the development material and electrically charge the material through triboelectric contact with the walls of said duct.

References Cited in the file of this patent UNITED STATES PATENTS Jacob July 3, 1956 rea-m'w 

